US6297634B1 - MRI magnetic field generator - Google Patents

MRI magnetic field generator Download PDF

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US6297634B1
US6297634B1 US09/486,873 US48687300A US6297634B1 US 6297634 B1 US6297634 B1 US 6297634B1 US 48687300 A US48687300 A US 48687300A US 6297634 B1 US6297634 B1 US 6297634B1
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temperature
magnetic field
permanent magnets
mri
field generator
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Masaaki Aoki
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Neomax Co Ltd
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Sumitomo Special Metals Co Ltd
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 
    • A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves  involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/383—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using permanent magnets
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/389—Field stabilisation, e.g. by field measurements and control means or indirectly by current stabilisation

Definitions

  • This invention relates to an improvement to a magnetic field generator used in a medical-use magnetic resonance imaging device (hereinafter referred to as an MRI device), and more particularly, this invention relates to an MRI-use magnetic field generator that controls the temperature of permanent magnets that serve as the magnetic field generation source by measuring the temperature of the permanent magnets and using a heating means or cooling means incorporated into base yokes or the like, so that any unevenness in the temperature distribution of the permanent magnets is efficiently reduced without any loss of uniformity in the magnetic field generated within an imaging space.
  • MRI device medical-use magnetic resonance imaging device
  • An MRI device is designed so that all or part of a patient's body is inserted into the cavity of a magnetic field generator that forms a powerful magnetic field, and a body section image of the desired area is obtained, allowing a graphic representation to be made even of the texture of the tissue of this area.
  • the cavity must be wide enough for all or part of the patient's body to be inserted, and a stable, powerful, and uniform magnetic field having a precision of at least 1 ⁇ 10 ⁇ 4 at 0.02 to 2.0 T usually must be formed within the imaging space inside the cavity for a sharp body section image to be obtained.
  • FIGS. 9A and 9B illustrate a known structure of a magnetic field generator used in an MRI device (Japanese Patent Publication H2-23010).
  • permanent magnets 30 which make use of R—Fe—B-based magnets as the magnetic field generation source, are fixed to the opposing sides of a pair of base yokes 35 , pole pieces 31 are fixed opposite one another on the various magnetic pole sides, and a static magnetic field is generated within the cavity 33 between the pole pieces 31 .
  • the illustrated magnetic circuit is achieved by connecting columnar support yokes 36 between the pair of flat base yokes 35 .
  • 37 in the figure is a tilt field coil
  • 38 is an imaging space formed in the center within the cavity 33 .
  • the pole pieces 31 are usually made from a flat bulk material (a single piece) produced by planing down electromagnetic soft iron, pure iron, or another such magnetic material.
  • a structure in which an annular protrusion 32 is provided around the periphery, or a protrusion is provided in the center (not shown) Japanese Utility Model Publication H5-37446, or the like may be employed in order to enhance the uniformity of magnetic field distribution within the cavity 33 .
  • permanent magnets are increasingly being utilized as the magnetic field generation source for forming a static magnetic field within the cavity 33 .
  • a drawback to these permanent magnets, however, is that the field intensity tends to vary with changes in the temperature due to the magnetic characteristics inherent to the magnets themselves.
  • the stability of the intensity of the static magnetic field formed in the cavity is important with an MRI device, and ways of keeping the field intensity stable include covering the entire magnetic field generator, or just the required portions, with an adiabatic material so that the permanent magnets are kept at a constant temperature, and providing cooling or heating means on the inside of the base yokes or the above-mentioned adiabatic material.
  • the temperature is controlled with a cooling apparatus in which electronic cooling elements that utilize the Peltier effect are disposed around the outer periphery of the base yokes (Japanese Utility Model Publication H3-56005).
  • a cooling apparatus in which electronic cooling elements that utilize the Peltier effect are disposed around the outer periphery of the base yokes (Japanese Utility Model Publication H3-56005).
  • the above-mentioned cooling apparatus cools the entire magnetic field generator to within a temperature range that is 10 to 50° C. lower than the ambient temperature, changes in the ambient temperature are moderated by an adiabatic material that surrounds the device, and the temperature is fine-tuned to a specific range.
  • the room temperature is usually kept at about 22 to 25° C. so that a clothed patient can be examined in comfort.
  • the structure described above requires that the MRI device be kept at all times at a temperature lower than room temperature, but this is impractical because of inefficiency from the standpoint of energy consumption, and because the structure for cooling the entire structure makes the device larger and more expensive than with the structure discussed below in which a heating means is provided.
  • a structure in which a heating means is provided makes it easier to obtain a compact and inexpensive device than the above-mentioned structure in which a cooling apparatus is provided, and is said to be more efficient in terms of energy consumption. Examples of such structures are known from Japanese Laid-Open Patent Applications S63-43649 and S63-278310.
  • any of various heating means are used to control the entire magnetic field generator to a temperature that is about 5 to 10° C. lower than the room temperature where the MRI device is installed.
  • the magnetic field generator shown in FIG. 10 is structured such that flat base yokes 42 are disposed across from one another via columnar support yokes 43 , permanent magnets 40 are fastened to the opposing sides thereof, and pole pieces 41 are provided to the magnetic pole sides thereof.
  • a planar heater 44 is disposed on the outer surface of each of the base yokes 42 , a planar heater (not shown) is also disposed on the inner surfaces of the adiabatic materials 45 , and these yokes are entirely covered with the adiabatic material 45 .
  • Japanese Laid-Open Patent Application S63-43649 proposes a structure in which planar heaters are disposed only on the inner surfaces of the above-mentioned adiabatic materials 45 .
  • the problem with this structure is that the temperature of the magnetic circuit is controlled by using a fan to forcibly send air heated by the planar heater through an air passage formed between the flat base yoke 42 and the adiabatic material 45 , so not only is the device complicated, but because the magnetic circuit is heated via air, the thermal efficiency is also poor.
  • An object of the invention of Japanese Laid-Open Patent Application S63-278310 is to solve the above problems, and as shown in FIG. 10, the thermal efficiency is improved somewhat by directly disposing the planar heaters 44 on the outer surfaces of the base yokes 42 on which the permanent magnets 41 are disposed.
  • the heaters 44 are disposed on the outer surfaces of the base yokes 42 , that is, on the sides opposite from the cavity-facing sides of the permanent magnets 40 , there is a pronounced tendency for the heat to be diffused from the magnetic circuit to the outside, so no improvement in thermal efficiency is realized.
  • Japanese Laid-Open Patent Application H8-266506 (U.S. Pat. No. 5,652,517) discloses a structure that improves on the invention discussed in Japanese Laid-Open Patent Application S63-278310.
  • the structure of Japanese Laid-Open Patent Application H8-266506 is characterized in that a thermally conductive material is attached, either directly or via a gas, to the side faces of upper and lower base yokes to which permanent magnets are attached.
  • the heater means in Japanese Laid-Open Patent Application H8-266506 is in the form of a sheet heater, and an AC sheet heater and a DC sheet heater are fixed one above the other to the side faces of the base yokes.
  • the fixing is accomplished by covering the AC sheet heater and the DC sheet heater with a fixing bake plate from above and bolting the plate down.
  • Japanese Laid-Open Patent Application H8-266506 states that the above structure affords improvements in thermal efficiency, control follow-up properties, and ease of work as compared to the structures disclosed in Japanese Laid-Open Patent Applications S63-43649 and S63-278310.
  • the present invention was perfected upon discovering that the thermal efficiency can be improved and operating costs can be reduced by incorporating the temperature control means (mainly just the heating means, or the heating means and heat radiating (cooling) means) into the base yokes where the permanent magnets are provided, for example, and that the follow-up properties of temperature control can also be enhanced by disposing the above-mentioned heating means or other such temperature control means in the vicinity of the permanent magnet.
  • the temperature control means mainly just the heating means, or the heating means and heat radiating (cooling) means
  • this invention is an MRI-use magnetic field generator that forms a magnetic circuit with magnetic path formation members and permanent magnets serving as magnetic field generation sources, and that generates a magnetic field within an imaging space, this MRI-use magnetic field generator having temperature control means incorporated into the permanent magnets and/or the magnetic path formation members.
  • the inventors also propose a structure in which temperature sensors are disposed in the permanent magnets and/or the magnetic path formation members, a structure in which there is a temperature regulator which controls the temperature of the temperature control means according to the temperature detected by the temperature sensors, and a structure having means for halting the temperature control means according to the temperature of the permanent magnets and/or the magnetic path formation members.
  • a structure in which, in an MRI-use magnetic field generator in which a pair of permanent magnets are disposed facing each other via a cavity, there are at least two control systems that independently control the various temperatures of the pair of permanent magnets.
  • FIG. 1A is a front view illustrating the structure of the MRI-use magnetic field generator of the present invention
  • FIG. 1B is a vertical cross section illustrating the main components in FIG. 1A;
  • FIG. 2 is an oblique view of the MRI-use magnetic field generator of the present invention
  • FIG. 3 is a vertical cross section illustrating the main components of another example of the MRI-use magnetic field generator of the present invention.
  • FIG. 4 is a vertical cross section illustrating the main components of another example of the MRI-use magnetic field generator of the present invention.
  • FIG. 5 is a partial vertical cross section illustrating the main components of the retaining means of the temperature control means used in the MRI-use magnetic field generator of the present invention
  • FIG. 6 is a partial vertical cross section illustrating the main components of the retaining means of the temperature control means used in the MRI-use magnetic field generator of the present invention
  • FIG. 7A is a top view illustrating the structure of a pole piece of the MRI-use magnetic field generator of the present invention, and FIG. 7B is a vertical cross section thereof;
  • FIG. 8 is a circuit diagram illustrating the temperature control of the MRI-use magnetic field generator of the present invention.
  • FIG. 9A is a partially cut-away front view illustrating the structure of a conventional MRI-use magnetic field generator, and FIG. 9B is a lateral cross section thereof;
  • FIG. 10 is a partially cut-away oblique view illustrating the structure of another conventional MRI-use magnetic field generator.
  • the MRI-use magnetic field generator that is the object of the present invention is not limited to the examples given below, and can be applied to any structure.
  • the present invention can also be applied to a structure in which a pair of flat base yokes are linked by a plurality of columnar support yokes, a structure in which a pair of opposing, flat base yokes are supported at one end by a flat support yoke, a structure in which pole pieces are disposed on the cavity-facing side of the permanent magnets that serve as the magnetic field generation source, a structure in which no pole pieces are provided, and so forth.
  • the magnetic field strength, magnetic field uniformity and size of the cavity required by the magnetic path formation member dimensions of the flat base yokes should be suitably selected according to each of the various properties.
  • Ferrite magnets, rare earth cobalt-based magnets, or another known magnet material can be used as the permanent magnets that serve as the magnetic field generation sources.
  • the device can be made much more compact by using an Fe—B—R-based permanent magnet in which R is a light rare earth such as Nd and Pr, which are abundant resources, and in which boron and iron are the main components, exhibiting an extremely high energy volume of 30 MGOe or higher.
  • R is a light rare earth such as Nd and Pr, which are abundant resources, and in which boron and iron are the main components, exhibiting an extremely high energy volume of 30 MGOe or higher.
  • a structure in which the above-mentioned known permanent magnets are disposed in combination allows a more economical magnetic field generator to be provided without increasing the size of the device.
  • the function of the support yokes is to mechanically support the base yokes and ensure the required cavity dimensions, as well as to form a magnetic path for forming a magnetic field within the cavity.
  • the material of which the pole pieces are made is not limited to the materials in the working examples. For instance, pure iron, or a soft magnetic powder that has been molded with an electrically resistant material, or the like can be employed.
  • the residual magnetism and eddy current generated at the pole pieces during application of a pulse field to the tilt field coils can be reduced by employing pole pieces made from a laminate of silicon steel sheets or from any of a variety of soft ferrites based on Mn—Zn, Ni—Zn, or the like, which have a low coercive force and high electrical resistance, or from a combination of these materials.
  • a laminate of silicon steel sheets is advantageous from a cost standpoint because it is less expensive than a soft ferrite.
  • the reduction in eddy current and residual magnetism will be better and the attachment work will be easier if, as shown in FIGS. 7A and 7B, in producing the pole piece 20 from the above-mentioned silicon steel sheets, a plurality of blocks 23 composed of laminates of silicon steel sheets are arranged on a magnetic material base 21 , and these blocks are further laminated.
  • Optimizing the thickness of the above-mentioned entire pole piece or the thickness ratio of the magnetic material base 21 ensures that the pole piece will have good mechanical strength, equalizes the field intensity required of the pole piece, and prevents eddy current and residual magnetism from occurring. It is also possible to employ a structure in which the magnetic material base 21 is not used by devising some means for fixing the blocks 23 composed of laminates of silicon steel sheets.
  • annular protrusion composed of electromagnetic soft iron, pure iron, or another such magnetic material ring around the periphery of the pole piece in order to enhance the field uniformity within the cavity.
  • the reduction in eddy current will be even better if one or more slits are provided to divide up the annular protrusion 22 in the circumferential direction as shown in FIGS. 7A and 7B.
  • the cross sectional shape of the annular protrusion is not limited to the rectangular shape shown in the figure, and may instead be approximately triangular, trapezoidal, or the like, with this shape being suitably selected as dictated by the required field intensity, field uniformity, and so forth. Disposing a protrusion 24 on the inside of the annular protrusion of the pole piece is also effective in terms of forming a uniform magnetic field.
  • pole pieces in not essential in the present invention.
  • drawbacks to the use of pole pieces such as a decrease in the field intensity within the cavity due to magnetic flux leakage from the side faces of the pole pieces, a decrease in the tilt field rise characteristics due to the eddy current generated within the pole pieces, and an increase in the weight of the overall magnetic circuit, so a structure in which no pole pieces are disposed is also effective in terms of avoiding these problems.
  • the structure in which no pole pieces are disposed can be, for example, the structure disclosed in Japanese Laid-Open Patent Application H3-209803, which was previously proposed by the inventors of the present invention.
  • Temperature control in the present invention is such that a temperature regulator operates according to the temperature detected by a temperature sensor, and in the heating or heat radiation (cooling) by the temperature control means, the temperature control means is incorporated into the permanent magnets themselves or into the pole pieces or base yokes disposed in the vicinity of the permanent magnets, so less heat is lost through radiation to the outside, the permanent magnets are heated and cooled extremely efficiently, and the follow-up properties of the control are good. Furthermore, partial temperature control with a plurality of control systems is possible by disposing a plurality of temperature sensors, an advantage of which is less decrease in the symmetry of the magnetic field uniformity.
  • the temperature control means incorporated into the permanent magnets, base yokes, pole pieces, etc., in the present invention is not limited to the structures illustrated in the working examples, and variety of structures can be employed so long as the temperature control means is disposed in holes formed in the permanent magnets, base yokes, pole pieces, etc., and these can be heated and cooled efficiently.
  • a structure in which the entire magnetic field generator is controlled to a temperature about 5 to 10° C. higher than the room temperature where the MRI device is installed is usually used at the present time.
  • a heating means as the temperature control means for reasons such as energy conservation, cost, and ease of operation.
  • the heating means must be in close contact with the members being heated, such as the base yokes.
  • the members being heated such as the base yokes.
  • a rod-shaped heating element is a particularly favorable device for the heating means because it can be easily inserted into holes formed in the permanent magnets, base yokes, and pole pieces, and is also easy to handle.
  • a rod-shaped heating element is a structure such as a tubular heater comprising a heating element held within a metal pipe, with the space inside this pipe filled with an insulator such as MgO. Iron, copper, aluminum, stainless steel, or another such metal or an alloy material can be used for the above-mentioned metal pipe.
  • FIG. 5 illustrates a retaining means 53 in the form of a bolt that is threaded into a hole formed in the base yoke 3 .
  • the rod-shaped heating element 10 that is inserted into the hole is held in place by the bolt-shaped retaining means 53 that strikes the end of a metal pipe 51 that constitutes the rod-shaped heating element 10 .
  • 52 is a lead wire going from the rod-shaped heating element 10 to the outside.
  • FIG. 6 illustrates a retaining means comprising a metal pipe 54 formed in an L-shape and disposed so that it strikes the end of the metal pipe 51 that constitutes the rod-shaped heating element 10 , and an attachment bracket 55 that fixes the metal pipe 54 to the base yoke 3 .
  • FIGS. 5 and 6 Various other structures besides the retaining means for a heating means consisting of a rod-shaped heating element shown in FIGS. 5 and 6 can also be employed.
  • threads may be formed around the outside of the metal pipe 51 that constitutes the rod-shaped heating element 10 , or a flange can be provided to the end of the metal pipe 51 for fixing the base yoke 5 , among other retaining means that can be employed.
  • cooling means can be used as the temperature control means in the present invention.
  • a means with a simple structure such as a heat pipe.
  • cooling can be accomplished by disposing a heat pipe in holes provided to the permanent magnets, base yokes, or other magnetic path formation members by the same method as with the heating means and actively causing heat to radiate to the outside, or cooling can be effected by introducing a coolant into the members via a heat pipe.
  • the temperature sensors disposed for temperature control in the present invention can be temperature sensing resistors, thermistors, or the like, with a known sensor being used as needed according to the structure of the temperature control system.
  • the temperature sensors may be disposed at suitable locations as dictated by the structure of the magnetic circuit, such as the permanent magnets, base yokes, and pole pieces.
  • the goal is achieved by disposing the temperature sensors on the surface of the permanent magnets, base yokes, or pole pieces. To detect the temperature at higher precision, it is favorable to form holes at specific locations of the various members mentioned above, and dispose the temperature sensors in these holes.
  • the temperature sensors are disposed at the pole pieces, it is preferable to dispose them in holes made at locations away from the tilt field coils, such as around the outsides of the annular protrusions, or in the centers of the pole pieces, since noise can be generated by the magnetic field generated by the tilt field coils.
  • any known electrical control means can also be employed for the temperature control of the permanent magnets by the above-mentioned temperature control means and temperature sensor.
  • a single control system may be used, or two or more systems may be used as needed.
  • a heating means with a large capacity can be used concurrently in order to shorten the time it takes to raise the temperature.
  • a temperature regulator having two types of output: one for fast temperature elevation and one for fine tuning so as to maintain the temperature setting.
  • the base yokes which have a relatively large surface area and greatly affect the temperature of the permanent magnet, should preferably have disposed around their periphery an adiabatic material for isolating the heat from the air. Furthermore, besides the base yokes, it is also favorable for the support yokes, permanent magnets, and pole pieces to be surrounded by an adiabatic material as needed.
  • means can be provided for halting the operation of the temperature control means should the temperature of the permanent magnets rise markedly higher than the specified temperature due to a malfunction of the above-mentioned temperature sensor or temperature regulator.
  • a thermostat for forcibly shutting off the current to the heater
  • a temperature fuse for forcibly shutting off current to the heater if the temperature exceeds 90° C., for example.
  • FIGS. 1A, 1 B, and 2 The characteristics of the present invention will now be described through reference to the examples illustrated in FIGS. 1A, 1 B, and 2 .
  • the magnetic field generator has magnetic path formation members, which constitute a magnetic circuit, disposed on a floor 1 via legs 2 .
  • the magnetic path formation members comprise a pair of flat base yokes 3 connected by four columnar support yokes 4 .
  • the magnetic field generation source consists of a pair of permanent magnets 5 featuring R—Fe—B-based magnets. These are attached to the opposing faces of the base yokes 3 , and pole pieces 6 are fixed to the respective pole piece faces, forming a cavity 8 in which a static magnetic field is generated between the pole pieces 6 .
  • An imaging space 9 is set up within the cavity 8 between the pole pieces 6 , and a specific, uniform magnetic field is generated within this space.
  • the pole pieces 6 that serve as magnetic path formation members each have an annular protrusion 7 in this structure, and are formed using the blocks of laminated silicon steel sheets illustrated in FIGS. 7A and 7B.
  • rod-shaped heating elements Holes that are the same length as rod-shaped heating elements are made in the center of the four side faces and the top face or bottom face of the base yokes 3 (made of pure iron) in order to insert the rod-shaped heating elements.
  • a plurality of rod-shaped heating elements (tubular heaters) 10 and 11 are inserted so as to be in close contact with holes formed in the base yokes 3 , and are connected to a temperature regulator via leads and relays (not shown).
  • these elements are connected to two-part temperature control systems 13 and 14 structured as shown in FIG. 8 .
  • control signals from temperature regulators 16 are sent to solid state relays 15 , with this signal representing the difference between the temperature setting and the temperature of the permanent magnets as detected by the temperature sensor 12 disposed around the outer periphery of the permanent magnets 5 .
  • Controlled current passes through the solid state relays 15 to the rod-shaped heating elements 10 and 11 , and suitable heating is performed according to the respective temperatures of the permanent magnets 5 .
  • a specified temperature is maintained, without any temperature unevenness occurring in the magnetic circuit, and particularly the entire permanent magnets.
  • the separate temperature control systems 14 and 14 shown in FIG. 8 must be provided to the upper and lower base yokes 3 .
  • the electrical circuit is structured such that there are independent control systems 13 and 14 , one for the temperature sensor 12 attached to the permanent magnet 5 disposed at the upper base yoke 3 and the rod-shaped heating element 10 incorporated into the upper base yoke 3 , and one for the temperature sensor 12 attached to the permanent magnet 5 disposed at the lower base yoke 3 and the rod-shaped heating element 10 incorporated into the lower base yoke 3 .
  • a plurality of rod-shaped heating elements 10 and 11 are connected to each of the control systems 13 and 14 . This is to prevent local heating of the magnetic circuit, and heat the overall circuit evenly. Also, although not shown in the figures, an adiabatic material for thermally isolating the magnetic circuit from the surrounding air can be suitably disposed.
  • the structure in FIG. 3 is such that a temperature control means consisting of a rod-shaped heating element 10 is incorporated not only the base yoke 3 , but also into the pole piece 6 .
  • an electrical circuit is configured such that the rod-shaped heating element 10 incorporated into the pole piece 6 and the temperature sensor 12 disposed on the pole piece 6 are integrated into a single control system.
  • the structure in FIG. 4 is such that the permanent magnet 5 forms a cavity for direct magnetic field generation.
  • a temperature control means consisting of a rod-shaped heating element 10 is incorporated into the base yoke 3 and the permanent magnet 5 , and a temperature sensor 12 is provided to the cavity-facing side of the permanent magnet 5 .
  • an electrical circuit is configured such that the rod-shaped heating element 10 incorporated into the permanent magnet 5 and the temperature sensor 12 disposed at the permanent magnet 5 are integrated into a single control system.
  • the temperature control means can be disposed in either the permanent magnets, the base yokes, or the pole pieces.
  • the temperature control means in the present invention is provided in order to control the temperature of the permanent magnets, and a structure in which it is directly provided to the permanent magnets is the most effective in terms of thermal efficiency.
  • thermocontrol means since heating more than necessary decreases the magnetic field intensity, controlling the temperature of the permanent magnets merely with temperature control means disposed at the permanent magnets cannot be considered a favorable structure.
  • a preferable structure makes use of temperature control means in the base yokes, pole pieces, and so on.
  • a structure in which the temperature control means is disposed at the base yokes is not necessarily good in terms of thermal efficiency because the temperature of the permanent magnet is controlled indirectly.
  • the base yokes have a much larger volume than the permanent magnets, and once they have been adjusted to a specific temperature, they are not readily affected by changes in the ambient temperature, so their temperature is more stable, and therefore the temperature of the permanent magnet connected to the base yokes can be easily kept constant. Also, because the base yokes are easier to machine than the permanent magnets, the holes in which the rod-shaped heating elements, heat pipes, etc., will be disposed can be formed at any location. It is therefore possible to keep the temperature uniform, without causing any temperature unevenness in the base yokes Themselves.
  • a structure in which the temperature control means is disposed at the pole pieces is not necessarily good in terms of thermal efficiency, either, because the temperature of the permanent magnet is controlled indirectly. Still, heating and cooling can be performed more efficiently than with a structure involving disposition at the base yokes because the volume of the pole pieces is smaller and is about the same as that of the permanent magnets. Furthermore, by controlling the temperature of the pole pieces, it is also possible to reduce the effect of temperature changes on the permanent magnets due to the generation of heat by the tilt field coils disposed in the vicinity of the pole pieces. In particular, by disposing a plurality of temperature control means at radial locations of the pole pieces, it is possible to keep the temperature even for the entire pole pieces.
  • the temperature control means it is also possible in the present invention for the temperature control means to be incorporated in either the permanent magnets, the base yokes, or the pole pieces. To keep the permanent magnets at a constant temperature, it is preferable to select the capacity, disposition location, disposition quantity, and so forth of the temperature control means after taking into account the various volumes, materials, and so on involved.
  • the illustrated structure makes use of a rod-shaped heating element as the temperature control means.
  • a cooling means featuring a heat pipe or the like.
  • a structure can be employed in which a cooling means is disposed at the permanent magnets, or in which heating means and cooling means are both disposed at the base yokes.
  • the target temperature of the upper and lower permanent magnets 5 was set to 32° C. by the two-part temperature control systems 13 and 14 shown in FIG. 8, whereupon the temperature differential between the upper and lower magnets could be held to 0.1° C., and the energy consumption was 600 W.
  • the structure of the present invention not only allows for high-precision temperature control, but also makes possible a major reduction in energy consumption.
  • the target temperature of the permanent magnets 5 was set to 32° C. by a four-part temperature control system in which temperature control means corresponding to the structure of FIG. 3 were also disposed at the pole pieces, whereupon it was confirmed that the temperature differential between the upper and lower magnets could be held to 0.1° C. even with respect to external temperature changes due to heat generated by the tilt field coils, etc.
  • the MRI-use magnetic field generator of the present invention is characterized by a structure in which temperature control means are embedded in the base yokes and 80 forth that make up the magnetic path formation members.
  • the temperature control means executes heating or cooling by means of a temperature regulator according to the temperature detected by temperature sensors, the permanent magnets disposed in the vicinity of the base yokes or the like are heated or cooled efficiently, and follow-up with respect to control signals is good.
  • a temperature control means such as a heater, embedded in the interior of the base yokes or the like
  • the heat generated by the heater is conducted through the base yokes, etc., and reaches the permanent magnets directly, so the heat is not diffused to the outside and lost, allowing temperature control to be performed extremely efficiently.
  • partial temperature control is possible by disposing a plurality of temperature sensors at the permanent magnets. Another advantage is that good symmetry can be achieved in the magnetic field uniformity by controlling the temperature through control of the temperature control means with a plurality of control systems independently provided to a plurality of permanent magnets.

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US09/486,873 1998-06-19 1999-06-16 MRI magnetic field generator Expired - Lifetime US6297634B1 (en)

Applications Claiming Priority (3)

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JP18971698 1998-06-19
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US6566880B1 (en) * 1998-09-11 2003-05-20 Oxford Magnet Technology Limited Stabilization of a magnetic field of a magnetic resonance imaging apparatus
US6577125B2 (en) * 2000-12-18 2003-06-10 Halliburton Energy Services, Inc. Temperature compensated magnetic field apparatus for NMR measurements
US6653835B2 (en) * 2000-09-26 2003-11-25 Siemens Aktiengesellshaft Magnetic resonance tomograph with a temperature controller for thermally highly sensitive components
US20040061067A1 (en) * 2002-08-02 2004-04-01 Leo Elecktronenmikroskopie Gmbh Particle-optical apparatus and method for operating the same
US20040074083A1 (en) * 2001-04-03 2004-04-22 General Electric Company Method and apparatus for magnetizing a permanent magnet
US6906517B1 (en) * 2004-09-28 2005-06-14 General Electric Company Method and apparatus for maintaining thermal stability of permanent magnets in MRI systems
US7023309B2 (en) 2001-04-03 2006-04-04 General Electric Company Permanent magnet assembly and method of making thereof
US20070216414A1 (en) * 2001-10-24 2007-09-20 Hitachi, Ltd. Nuclear magnetic resonance spectrometer for liquid-solution
US20070290685A1 (en) * 2006-06-12 2007-12-20 Qiang He Temperature control method for a permanent magnet arrangement of a magnetic resonance system
US20080048656A1 (en) * 2006-07-14 2008-02-28 Fengshun Tan Thermal controlling method, magnetic field generator and mri apparatus
US20080303522A1 (en) * 2004-07-01 2008-12-11 Masaaki Aoki Magnetic Field Generator
US20090128269A1 (en) * 2007-11-15 2009-05-21 General Electric Company Cooling system and apparatus for controlling drift of a main magnetic field in an mri system
US20110037471A1 (en) * 2009-08-12 2011-02-17 Seiji Nozaki Magnetic resonance imaging apparatus
US20150137922A1 (en) * 2012-07-02 2015-05-21 Hitachi Metals, Ltd. Magnetic Circuit
US20170227973A1 (en) * 2016-02-09 2017-08-10 Siemens Healthcare Gmbh Method for operating a temperature control, apparatus for a medical examination apparatus, a temperature control apparatus, and a medical examination apparatus
US20180364181A1 (en) * 2017-06-15 2018-12-20 Korea Basic Science Institute Wafer inspection apparatus

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US7962019B2 (en) * 2007-11-09 2011-06-14 General Electric Company System, method and apparatus for controlling drift of a main magnetic field in an MRI system
CN101451967B (zh) * 2007-12-04 2012-05-09 西门子（中国）有限公司 改善核磁共振成像设备的成像质量的方法及设备
JP2011217913A (ja) * 2010-04-08 2011-11-04 Mr Technology:Kk 温度制御方法及び装置
JP5754010B2 (ja) * 2011-06-20 2015-07-22 学校法人金沢工業大学 軽量永久磁石型磁気共鳴分析装置
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US6566880B1 (en) * 1998-09-11 2003-05-20 Oxford Magnet Technology Limited Stabilization of a magnetic field of a magnetic resonance imaging apparatus
US6653835B2 (en) * 2000-09-26 2003-11-25 Siemens Aktiengesellshaft Magnetic resonance tomograph with a temperature controller for thermally highly sensitive components
US6577125B2 (en) * 2000-12-18 2003-06-10 Halliburton Energy Services, Inc. Temperature compensated magnetic field apparatus for NMR measurements
US7023309B2 (en) 2001-04-03 2006-04-04 General Electric Company Permanent magnet assembly and method of making thereof
US20040074083A1 (en) * 2001-04-03 2004-04-22 General Electric Company Method and apparatus for magnetizing a permanent magnet
US7053743B2 (en) 2001-04-03 2006-05-30 General Electric Company Permanent magnet assembly and method of making thereof
US7345560B2 (en) 2001-04-03 2008-03-18 General Electric Company Method and apparatus for magnetizing a permanent magnet
US6891375B2 (en) * 2001-07-04 2005-05-10 Ge Medical Systems Global Technology Company, Llc Static field controlling method and MRI apparatus
US20030006771A1 (en) * 2001-07-04 2003-01-09 Takao Goto Static field controlling method and MRI apparatus
US20070216414A1 (en) * 2001-10-24 2007-09-20 Hitachi, Ltd. Nuclear magnetic resonance spectrometer for liquid-solution
US7492159B2 (en) * 2001-10-24 2009-02-17 Hitachi, Ltd. Nuclear magnetic resonance spectrometer for liquid-solution
US20040061067A1 (en) * 2002-08-02 2004-04-01 Leo Elecktronenmikroskopie Gmbh Particle-optical apparatus and method for operating the same
US6914248B2 (en) 2002-08-02 2005-07-05 Carl Zeiss Nts Gmbh Particle-optical apparatus and method for operating the same
US20080303522A1 (en) * 2004-07-01 2008-12-11 Masaaki Aoki Magnetic Field Generator
US7733090B2 (en) * 2004-07-01 2010-06-08 Hitachi Metals, Ltd. Magnetic field generator
US6906517B1 (en) * 2004-09-28 2005-06-14 General Electric Company Method and apparatus for maintaining thermal stability of permanent magnets in MRI systems
US7432708B2 (en) * 2006-06-12 2008-10-07 Siemens Aktiengesellschaft Temperature control method for a permanent magnet arrangement of a magnetic resonance system
US20070290685A1 (en) * 2006-06-12 2007-12-20 Qiang He Temperature control method for a permanent magnet arrangement of a magnetic resonance system
US20080048656A1 (en) * 2006-07-14 2008-02-28 Fengshun Tan Thermal controlling method, magnetic field generator and mri apparatus
US7639013B2 (en) 2006-07-14 2009-12-29 Ge Medical Systems Global Technology Company, Llc Thermal controlling method, magnetic field generator and MRI apparatus
US20090128269A1 (en) * 2007-11-15 2009-05-21 General Electric Company Cooling system and apparatus for controlling drift of a main magnetic field in an mri system
US7868617B2 (en) * 2007-11-15 2011-01-11 General Electric Co. Cooling system and apparatus for controlling drift of a main magnetic field in an MRI system
US20110037471A1 (en) * 2009-08-12 2011-02-17 Seiji Nozaki Magnetic resonance imaging apparatus
US8547102B2 (en) * 2009-08-12 2013-10-01 Kabushiki Kaisha Toshiba Magnetic resonance imaging apparatus
US8922213B2 (en) 2009-08-12 2014-12-30 Kabushiki Kaisha Toshiba Magnetic resonance imaging apparatus
US20150137922A1 (en) * 2012-07-02 2015-05-21 Hitachi Metals, Ltd. Magnetic Circuit
US9576712B2 (en) * 2012-07-02 2017-02-21 Hitachi Metals, Ltd. Magnetic circuit for magnetic field generator
US20170227973A1 (en) * 2016-02-09 2017-08-10 Siemens Healthcare Gmbh Method for operating a temperature control, apparatus for a medical examination apparatus, a temperature control apparatus, and a medical examination apparatus
US10310523B2 (en) * 2016-02-09 2019-06-04 Siemens Healthcare Gmbh Method for operating a temperature control, apparatus for a medical examination apparatus, a temperature control apparatus, and a medical examination apparatus
US20180364181A1 (en) * 2017-06-15 2018-12-20 Korea Basic Science Institute Wafer inspection apparatus
US10641714B2 (en) * 2017-06-15 2020-05-05 Korea Basic Science Institute Wafer inspection apparatus

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WO1999065392A1 (fr) 1999-12-23
DE69935702T2 (de) 2007-12-27
CN1272774A (zh) 2000-11-08
KR100370444B1 (ko) 2003-01-30
JP2008237936A (ja) 2008-10-09
KR20010023038A (ko) 2001-03-26
EP1004270A4 (en) 2006-01-11
CN1257701C (zh) 2006-05-31
JP4203615B2 (ja) 2009-01-07
JP4356080B2 (ja) 2009-11-04
DE69935702D1 (de) 2007-05-16
EP1004270B1 (en) 2007-04-04
EP1004270A1 (en) 2000-05-31

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